Two-stage conversion of coal to liquid hydrocarbons



United States Patent US. Cl. 208 12 Claims ABSTRACT OF THE DISCLOSURE Coal is hydrogenated to produce liquid products in two stages. The first stage is an initial mild conversion by hydrogen-donor extraction followed by a second stage of catalytic hydrogenation using a cobalt molybdate catalyst and added molecular hydrogen. By this sequence, conversion of oxygen to CO rather than H O is maximized, thus more efficiently using the hydrogen to form hydrocarbon products. The liquid products may be hydrocracked in contact with a catalyst similar to that used in catalytic hydrogenation, so that the spent hydrocracking catalyst can be employed as the catalyst in the catalytic hydrogenation stage.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to the conversion of coal into liquid hydrocarbon products, by reacting hydrogen with the chemical constituents of coal both by hydrogen-donor solvent reaction and by catalytic hydrogenation.

Description of the prior art There has been much activity in the field of conversion of coal into liquid products, both in the field of hydrogen-donor extraction and in the catalytic hydrogenation of coal in an extract solution. In Gorin Patent 3,143,089, coal is converted into liquid products which are then hydrocracked and post-treated to form gasoline. In the Gorin process, coal is slurried in a solvent extraction zone with a suitable solvent, such as tetralin (a hydrogen-donor solvent). Catalytic hydrogenation may also be used in this extraction zone. However, after a partial conversion of the coal in the extraction zone, only the liquid products are then subjected to catalytic hydrogenation in succeeding zones, the unreacted coal from the extraction zone being passed into a carbonization zone where it is thermally reduced to char and cracked products. By the present invention, the unreacted coal from the extraction zone is separately subjected to a catalytic hydrogenation.

SUMMARY OF THE INVENTION An improved method of converting coal to liquid hydrocarbons comprises subjecting the coal to mild conversion by hydrogen-donor extraction followed by a second-stage catalytic hydrogenation. By this process, a higher overall conversion of coal is attained than is attainable by hydrogen-donor extraction alone, and the reagent hydrogen is utilized in a more efiicient manner than in the single-stage process.

In the first stage, oxygen is eliminated about equally as carbon dioxide (1.0 part) and water (1.5 parts). In the second stage (catalytic hydrogenation) the oxygen primarily reacts with hydrogen to leave in the form of Water rather than CO However, the constituents of the coal which contain the larger amounts of combined oxygen are reacted in the first stage. Since most of the oxy- 3,488,279 Patented Jan. 6, 1970 gen has been removed in the first stage, the consumption of hydrogen to form water is minimized.

BRIEF DESCRIPTION OF THE DRAWING By advertence to the drawing, wherein the present process is schematically set forth, it is seen that the process involves the preparation of a slurry in the zone by admixture of crushed coal introduced by way of line 102 with a hydrogen-donor solvent introduced by way of line 104. The slurry is removed by way of line 106 and is passed into a hydrogen-donor extraction zone 10%, wherein the slurry is maintained under conversion conditions, as more specifically set forth hereinafter. The liquid products are separated from the unreacted coal by mechanical separation, such as a hydroclone, and the liquid products are withdrawn from the extraction zone by way of line 110. The gas make is removed by way of line 112 for conversion into hydrogen (e.g., by the water-gas reaction), after removal of any components, such as butanes, pentanes, etc., which have economic values as motor fuels.

The unreacted coal and ash in an oil slurry are removed from the hydrogen-donor extraction zone 108 by way of line 114 and are passed into a catalytic hydrogenation zone 116 where the unreacted coal is contacted with a catalyst introduced intermittently or continuously by Way of line 118, and hydrogen which is continuously introduced by way of line 120. The hydrogenation is carried out in the liquid phase in the presence of liquid products produced by catalytic hydrogenation of the unreacted coal.

The liquid products from the catalytic hydrogeneration zone are withdrawn by way of line 122 and combined with the liquid products from the hydrogen-donor extraction zone and the combined stream is passed by way of line 124 to an atmospheric pressure pipestill 126, where the combined liquid products are fractionated into naphtha and heating oil (e.g., 450-600 F.) fractions. Atmospheric tower bottoms are carried by line 127 and introduced into a vacuum pipestill for separation into heavy gas oil (e.g., 600-950 F.) and heavy vacuum bottoms (950 F.+). The heavy gas oil is in part recycled to serve as a hydrogen-donor solvent (via line 104) and the remainder is hydrocracked in zone 130, preferably in a fixed-bed catalytic reaction. The heavy bottoms is in part passed to fuel by line 132 and the remainder is hydrocracked in zone 134 in either a fixed bed or liquid-fluidized bed catalytic reaction. Liquid hydrocracked products from both zones are combined for fractionation and recovery of motor fuel and other fractions. Spent catalyst from both hydrocracking zones may be conducted (e.g., by a slurry line 118) intermittently or continuously into zone 116.

Spent catalyst and some occluded oil are removed from the bottom of catalytic hydrogenation zone 116 by way of line 140, and the oil is preferably recovered by filtration. The fine ash and char, plus the occluded oil, are removed from the upper part of the zone 116, and the oil is recovered by filtration. Gas from the catalytic hydrogenation zones is withdrawn by way of line 142 and preferably is combined with the gas make 112 from hydrogen-donor extraction for passage to the hydrogen generator. Likewise, the offgas from the hydrocracking units is passed by way of lines 144 and 145 for admixture with the gas make from the reaction zones or possibly for other treatment to increase the hydrogen purity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS High conversions of coal are achieved in the present two-stage process. The first conversion stage is a hydrogen-donor extraction reaction, which eliminates most of the oxygen in the coal as C The second conversion stage is a catalytic hydrogeneration zone which can achieve a high conversion (greater than 90%, based on the unreacted coal which has been charged thereinto) but which tends to react oxygen with hydrogen, an inefficient way to use the expensive hydrogen reactant. The elimination of oxygen in the first stage, however, minimizes the consumption of hydrogen in the catalytic hydrogenenation zone since little oxygen remains for reaction with hydrogen.

FEEDSTOCK The present invention is directed to the conversion of a solid carbonaceous material (such as coal) into liquid hydrocarbon products, which products can (by hydrocracking and other means) be converted into gasoline and valuable hydrocarbon end products.

By the term coal is meant lignite, brown coal, subbituminous coal and bituminous coal. Suitable sources for these feedstocks are found in the natural deposits throughout the world, an example being the Illinois No. 6 seam.

Before introduction into the conversion system of the present invention, the coal should be reduced to a particle size distribution having a maximum particle size passing through an 8 mesh Tyler screen.

HYDROGEN-DONOR EXTRACTION The first reaction zone is devoted to the hydrogendonor extraction of the comminuted coal. It has been found that in hydrogen-donor type extractions, the oxygen in the coal is eliminated about equally as CO and H 0. By contrast, where the coal is catalytically hydrogenated, the ratio of CO to H O is about 1:5. Thus, the reaction of oxygen in the coal in the catalytic hydrogenation is preferentially directed to the formation of water, increasing the consumption of hydrogen without increasing the yield of hydrocarbon product. Thus, it is desirable to have the first-stage conversion carried out by hydrogen-donor extraction so that the great preponderance of oxygen in the coal (about 80-85 weight percent of the oxygen present) will be removed in the type of reaction where the consumption of hydrogen to form water is minimized. In the hydrogen-donor extraction zone, the comminuted coal is contacted with a solvent boiling in the general range 600-950 F., consisting of various partially hydrogenated aromatics, such as tetralin and the corresponding 3 and 4 ring aromatics. The solvent may comprise an admixture of substances which contains a suitable quantity of the desired hydrogen-donor solvent. For example, a stream boiling within the range of 600-950 F. is preferred, though a wider range of 450950 F. may also be used as the hydrogen-donor solvent.

Reaction conditions in the hydrogen-donor extraction zone will include a solvent-to-coal Weight ratio within the ratio within the range from about 1:1 to about 4:1, preferably about 1:1 to 2:1; a temperature within the range of about 650 F. to about 850 F., preferably 700-750 F.; a pressure chosen to maintain the solvent predominantly in the liquid phase at the temperature of operation, usually within the range from about 50 to about 800 p.s.i.g., preferably about 350 p.s.i.g. (depending on the vapor pressure of the chosen solvent), and an average residence time for the coal in the extraction zone within the range from about 0.25 to about 2.0 hours, preferably 0.5 hour. In this first-stage reaction zone, a coal conversion (based on moisture and ash-free coal) is obtained which is suitably Within the range from about 50 to 85 weight percent, preferably about 80 weight percent. Also, from about 70 to 90 weight percent of the oxygen present in the coal will be removed, preferably about 85 Weight percent. The liquid products obtained are removed from the solvent extraction zone, together with the solvent, and .may be fractionally separated therefrom to provide a recycle solvent stream which may be separately hydrogenated before return to the extraction zone, or preferably the solvent and liquid product are passed together through the subsequent treating facilities for hydrocracking. A recycle stream is obtained by fractionation of the hydrocracked products. Hydrogen added in the hydrocracking zone replaces the hydrogen withdrawn in the extraction zone.

If desired, molecular hydrogen or a gas stream containing molecular hydrogen may also be admitted into the hydrogen-donor extraction zone to provide a hydrogen partial pressure within the range from about 500 to about 1500 p.s.i.g.

CATALYTIC HYDROGENATION The unreacted coal char contains a lower percentage of combined oxygen than the original MAF coal. Usually, the percentage of oxygen in the unreacted coal char will be about 10-30% of the percentage in the original MAF coal.

At least a portion of the solvent and liquid products of the hydrogen-donor extraction is separated from the ash and unreacted coal which are present in the effluent from the extraction zone. This may be done mechanically, preferably by using a hydroclone-type separator. The ash and unreacted coal, suitably as a sludge or slurry with a portion of the liquid from the extraction zone, are introduced into a catalytic hydrogenation zone for further conversion of the coal. Suitably, the catalyst is maintained in the form of a liquid-fluidized bed or is entrained in the liquid stream to avoid the plugging which might occur in a fixed-bed operation.

The liquid which supports the catalyst and acts as a diluent can be supplied by increasing the amount of solvent and extract products carried from the extraction zone with the ash and unreacted coal. Preferably, however, the liquid is provided by reaction of unreacted coal with hydrogen in the catalytic hydrogenation zone. During startup of the unit, liquid is preferably supplied by solvent and extract from the hydrogen-donor extraction zone.

Generally speaking, the weight ratio of the liquid medium to the unreacted coal will be within the range of 1:1 to 4:1, preferably about 1:1 to 2:1. Reaction conditions Within the catalytic hydrogenation zone will include a temperature of 650-850 F., preferably 800 F., a pressure within the range of 1500-3500 p.s.i.g., preferably 2000 p.s.i.g., and a residence time for the coal within the range from about 0.1 to 1 hour, preferably 0.25 hour. Recycle gas, containing more than 75 mol percent hydrogen, is introduced into the reaction zone at a rate of from 25 to 75M s.c.f./ ton MAF coal, preferably 50M s.c.f./ton. (M s.c.f. means thousand standard cubic feet) As will be seen hereinafter, the catalyst which is used in the catalytic hydrogenation zone is preferably obtained as spent catalyst from a hydrocracking unit wherein the heavy liquid products, after hydrogen-donor extraction and catalytic hydrogenation, are treated with hydrogen for hydrocracking into lower boiling products (for example, gasoline).

In the catalytic hydrogenation reactor, the final conversion of -95% may be obtained without excessive cracking. Although normally most of the oxygen leaves a catalytic reactor in the form of H 0 rather than CO most of the oxygen has been removed in the first stage and the consumption of hydrogen to form water is minimized.

As an example of the process of the present invention, the following calculated example is given.

EXAMPLE A sub-bituminous coal having the proximate and ultimate analyses given in Table I below is finely divided to obtain a particle size distribution as shown in that table.

TABLE I Proximate analysis: Weight percent Moisture 21.20 Ash 8.55 Volatiles 35.55 Fixed carbon 34.70

Total 100.00

Ultimate analysis:

Moisture 21.20 Ash 8.55 Hydrogen (ex H O) 3.82 Carbon 50.98 Nitrogen 0.74 Sulfur 0.65 Oxygen (ex H O) 14.06

Total 100.00

1 This is equivalent to 20% oxygen based on MAF coal.

The finely divided coal described in Table I is admixed with tetralin in a weight ratio of solvent to coal of about 2:1. The slurry is admixed in a hydrogen-donor extraction zone at a temperature of about 825 F., and a pressure of about 750 p.s.i.g., and is reacted for a residence time of about 0.5 hour with the hydrogen-donor solvent (tetralin) to obtain a conversion of the coal of about 80 weight percent on a MAP basis. In this hydrogen-donor extraction zone, about 85 weight percent of the combined oxygen in the coal is removed in the gas phase, at an H O to CO weight ratio of about 1.5 :1. The liquid products of the hydrogen-donor reaction are removed along with the hydrogen-depleted solvent, and are later separated from the solvent so that the liquid products may be hydrocracked.

The 20% of the coal which is unreacted contains about 12 wt. percent 0 on a MAF basis, or only about 15% of the oxygen originally charged with the fresh coal. It (along with ash) is charged to a catalytic hydrogenation zone in contact with a cobalt molybdate catalyst and molecular hydrogen. The hydrogenation is carried out under a temperature of about 825 F., a pressure of about 2000 p.s.i.g., a solids residence time of about 0.5 hour, and a hydrogen feed rate of about 50M s.c.f./ton MAF char fed to reactor.

In this hydrogenation zone, a conversion of the coal feed is carried to 90 to 95 Weight percent, and the remaining oxygen is withdrawn mainly as water, the

weight ratio being about 5.011. Thus, in the first zone 85% of the oxygen is converted (51% conversion to Water, 34% conversion to CO and in the second zone the remaining 15 is converted (12.5% to water, 2.5% to C0 The total conversion to CO is 36.5%, compared to only about 16% if catalytic hydrogenation alone is employed.

The overall conversion of coal, in both reaction zones, is about 98-99 weight percent.

The liquid products withdrawn from the catalytic hydrogenation zone are admixed with the liquid products from the hydrogen-donor extraction and are fractionated, then subjected to hydrocracking in contact with a cobalt molybdate catalyst. If hydrocracked in a liquid-fluidized bed, the recycle gas rate is about 10,000 s.c.f./b., at a temperautre of about 800 F., and a pressure of about 2000 p.s.i.g.

The catalyst after having become spent in the hydrocrackin-g unit may be transformed to the catalytic hydrogenation reactor for use in hydrogenating the unreacted coal from the hydrogen-donor extraction zone.

By the present invention, the use of hydrogen-donor extraction in the first stage allows the use of low temperature and relatively low conversion rates to minimize gas yields and maximize removal of oxygen as CO both aspects contributing to the conservation of hydrogen (which desirably will react with the carbonaceous material in the coal to obtain a liquid hydrocarbon product). In the catalytic hydrogenation zone, higher temperatures are employed in order to obtain higher conversion and, by use of a catalyst, good selectivity toward liquid products.

It is thus submitted that the present invention provides a superior process for reducing the solid material in coal to liquid products suitable for commercial use.

Having disclosed my invention and a preferred embodiment thereof, what is desired to be obtained by Letters Patent is set forth in the following claims.

I claim: 1. A process for converting into liquid hydrocarbon products a solid, hydrogen-deficient, hydrocarbonaceous material containing combined oxygen which comprises: contacting said solid hydrocarbonaceous material in a non-catalytic hydrogen-donor extraction zone with a hydrogen donor solvent under conditions chosen to convert from 50 to weight percent of said solid hydrocarbonaceous material into liquid products and to remove from 70 to weight percent of the oxygen content thereof, thereafter contacting the unreacted solid hydrocarbonaceous material in a catalytic hydrogenation zone with gaseous molecular hydrogen and a hydrogenation catalyst under conditions chosen to obtain an overall conversion of to 99 weight percent of the solid hydrocarbonaceous material into liquid products to remove substantially all of the combined oxygen remaining therein. 2. A method in accordance with claim 1 wherein the unreacted solid hydrocarbonaceous material is separated from at least a portion of the liquid products and hydrogen-donor solvent before hydrogenation thereof in said catalytic hydrogenation zone.

3. A method in accordance with claim 1 wherein the solid hydrocarbonaceous material is lignite.

4. A method in accordance with claim 1 wherein the solid hydrocarbonaceous material is sub-bituminous coal. 5. A process for converting coal chosen from the group consisting of lignite, brown coal, sub-bituminous coal and bituminous coal, containing combined oxygen, into liquid hydrocarbon products which comprises contacting said coal in a non-catalytic hydrogen-donor extraction zone with a hydrogen-donor solvent under conditions chosen to convert from 50 to 85 weight percent of said coal into liquid products, and to remove a majority of the combined oxygen therein,

thereafter contacting the unreacted coal in a catalytic hydrogenation zone with gaseous molecular hydrogen and a hydrogenation catalyst under conditions chosen to obtain an overall conversion of 95 to 99 weight percent (base on MAF coal feed to the hydrogen-donor extraction zone) into liquid products, and to remove substantially all of the combined oxygen remaining therein.

6. A method in accordance with claim 5 wherein the unreacted coal is separated from at least a portion of the hydrogen-donor solvent and liquid products before hydrogenation of the unreacted coal in the catalytic hydrogenation zone.

7. A method in accordance with claim 5 wherein the coal is lignite.

8. A method in accordance with claim 5 wherein the coal is sub-bituminous coal.

9. A method in accordance with claim 5 wherein the hydrogenation catalyst is cobalt molybdate on alumina.

10. A process for converting coal into liquid hydrocarbon products which comprises subjecting a coal feedstock chosen from the group consisting of lignite,

brown coal, sub-bituminous coal, and bituminous coal,

7 having a particle size distribution within the range from .001 to 0.070 inch, preferably less than 0.04 inch maximum size, first to a non-catalytic hydrogen-donor extraction and then to a catalytic hydrogenation,

said hydrogen-donor extraction being carried out with a solvent chosen from the group consisting of tetralin, partially hydrogenated anthracene or aromatic liquid products boiling in the range of 400950 F., at a solvent-to-coal weight ratio within the range of 0.5 to 4, preferably 1-2: 1, at a temperature within the range of 650-850 F.,

preferably 700-750 F., at a pressure within the range of 50 to 800 p.s.i.g.,

preferably 350 p.s.i.g., and for a residence time within the range of 0.25

to 2 hours, preferably 0.5 hour, to obtain a coal conversion of 50 to 85 weight percent,

preferably 80 weight percent, and said catalytic hydrogenation being carried out under conditions comprising an elfective amount of a catalyst chosen from the group consisting of cobalt molybdate on alumina and the sulfided modifications thereof, a temperature within the range of 650 to 850 F., preferably 800 F., a pressure within the range of 1500 to 3500 p.s.i.g.,

preferably 2000 p.s.i.g., with a coal residence time within the range from 0.1 to 1 hour, preferably 0.25 hour, and a hydrogen feed rate of from 25 to 75 M s.c.f./ton of coal, preferably 50 M s.c.f./ton. 11. A method in accordance with claim wherein the coal is lignite or sub-bituminous coal,

the hydrogen donor extraction conditions include a solvent derived from the coal liquid products boiling in the range of 400-950 F., and a solvent-to-coal weight ratio of about 2:1, a temperature of about 700-750 F., a pressure of about 350 p.s.i.g., and a lignite residence time'of about 0.5 hour, whereby a conversion of about 85 weight percent is obtained, said catalytic hydrogenation conditions comprise a temperature of about 825 F., a pressure of about 2000 p.s.i.g., and a hydrogen feed rate of about M s.c.f./ton of char.

12. A method in accordance with claim 10 further comprising the steps of combining the liquid products from the hydrogen-donor extraction zone and the catalytic hydrogenation zone, and

hydrocracking at least a portion of the combined stream in contact with a cobalt molybdate catalyst under hydrocracking conditions comprising a temperature of about 750-800 F., a pressure of 1500 to 2500 p.s.i.g., and

a hydrogen treat rate of about 10,000 s.c.f./b.

References Cited UNITED STATES PATENTS 3,143,489 8/1964 Gorin 208-10 3,162,594 12/1964 Gorin 208-10 3,184,401 5/1965 Gorin 2088 2,464,271 3/1949 Storch 20810 3,275,546 9/1966 Retallick 20810 2,215,206 9/1940 Biggs et a1. 208-10 DELBERT E. GANTZ, Primary Examiner V, OKEEFE, Assist-ant Examiner US. Cl. X.R. 2088, 112 

